In recent years, FRP (Fiber Reinforced Plastics) cylinders have been used in various industrial fields. As a method for producing an FRP cylinder, a filament winding method (in Japanese Unexamined Patent Publication No. 2006-62355) in which carbon fibers are wound around a mandrel while being impregnated with a resin and a prepreg method (in Japanese Unexamined Patent Publication No. 2001-96635) in which a plurality of prepregs, each of which is made from carbon fibers impregnated with a thermosetting resin sheet, are wound and thermally cured to be formed as a plurality of FRP layers, are known in the art.